In P6 Professional, you can plot an S-curve to review the cost distribution of a cost-loaded schedule.
A project is a project; all projects share similar generic properties. Empirical data demonstrate the project attributes that drive success, which is what you want. One key attribute is the distribution of cost loading across the project lifecycle.
A well-planned project’s cost-loading shows cumulative planned cost versus time in a classic “S” shape: a slow initial ramp-up (mobilization), a steep middle curve (peak work) and a flattening tail-off (closure). S-curve red flags spotlight poor cost distribution, predict cash flow issues and expose unreliable earned value management (EVM) baselines for funding and performance forecasts.
Some warning signs include: front-heavy loading (too much spending early on), back-heavy loading (minimal initial spend, e.g., <10% in the first half, followed by a late spike that hides true risk), non-S shapes (linear curves that do not reflect real project flow) and lumpy distribution (big costs on single tasks, inflating later variances).
This article demonstrates how to create S-curve plots for comparing the baseline and current schedule cost distributions in P6 Professional.
Demonstration
Figure 1 displays our demonstration lump-sum cost-loaded schedule and its baseline.
In the BL Project Labor Cost column, we list the initial budgeted cost for each lump-sum task and in the adjacent Budgeted Labor Cost column is the current budget. At present, the current budget and baseline budget are equal. We want to plot the cost-loading of this schedule versus time. We proceed by clicking the Resource Usage Profile button in the bottom layout tool group, as shown in Figure 2.
Then, in the bottom left frame, we choose Display | Filter By | Current Project’s Resources, Figure 2. This displays a histogram of the LUMPSUM resource’s cost-loading distribution, Figure 3, lower-right frame.
We want the value of each column labeled. In the lower right frame, Figure 3, (1) we right-click (star stamp), then (2) from the pop-up menu left-click (circular stamp) the Resource Usage Profile Options menu item. In the Resource Usage Profile Options dialogue, we select the Graph tab, Figure 4.
Then, in the Figure 5 Graph tab, Display Additional Options, we check Show Values and click OK, Figure 5.
Now our histogram displays the precise budget for each week in our Month/Week timescale, as shown in Figure 6.
We again right-click the lower-right frame and choose Resource Usage Profile Options from the pop-up menu, as shown in Figure 6. In Figure 7, Resource Usage Profile Options dialogue, Data tab, and Show Bars/Curves section, we check the box to display the Budgeted Cumulative data.
In Figure 7, we also change the color of the Budgeted Cumulative data to orange. The S-curve for the schedule is plotted in Figure 8.
In Figure 8, first, note that we chose the Month/Week Time Scale so that weekends do not appear as flat horizontal lines during these nonworking periods. Second, in Figure 8, note that we could also have plotted the Budgeted, By Date, data histogram on the same graph. But this would have hidden parts of our S-curve, so we decided to display it separately.
When we inspect the S-curve in Figure 8, we discover that it is too linear; it does not reflect reality, and it needs more “S”- shaped curvature.
Adjust Cost-Loading
We therefore adjust the cost-loading of our schedule. Observe the updated LUMPSUM current budget values listed in the Budgeted Labor Cost column, Figure 9.
In Figure 9, we also selected the Install Piping & Couplings task in the task table and, in the bottom Resources tab, assigned the Front-Loaded curve to it. Though this does not help our “S”- shaped curvature, it is more realistic for an effort with a large upfront material cost. Again, our goal is to describe the true cost-loading distribution required to successfully execute the work.
After updating the current budget for our schedule, we want to plot the current budget’s S-curve and compare it to the baseline’s S-curve. To plot and compare these two S-curves on one graph, we must select the Activity Usage Profile from the bottom layout toolbar, as shown in Figure 10.
Then, in Figure 10, we (1) right-click the graph and (2) choose Activity Usage Profile Options. Before plotting the S-curves, we want to compare the histograms of the current and baseline budgets. To do this, we check the Baseline, By Date, and Budgeted, By Date options, then click Apply in Figure 11.
Figure 11 displays a histogram of the Baseline (blue) and the current Budgeted (orange). This helps us assess how the cost distribution was reallocated from the baseline to the update. Now, to plot the S-curves, we uncheck the By Dates options, place checkmarks in the Cumulative options for the Baseline and Budgeted cost data and click Apply, as shown in Figure 12.
Figure 12 displays plots of the Baseline S-curve, blue plot, and Budgeted S-curve (updated cost-loading), orange plot. From Figure 12, we begin to see a clearer “S” shape, more indicative of the true cost-loading of successful projects.
But to smooth the data points and create a presentation-ready, more telling graph, we need to copy and paste our data into Excel. We proceed by (1) clicking the Activity Usage Spreadsheet in Figure 13.
Then, in the bottom right frame next to the Timescale, we (2) right-click and (3) choose Spreadsheet Fields from the pop-up menu, Figure 13. In the Fields dialogue, from the Cumulative Available Options, select the Cum Budgeted Labor Cost and Cum BL Project Labor Cost, then click OK, as shown in Figure 14.
We select (or highlight) the Cum Budgeted Labor Cost (Cum Budgeted) and the Cum BL Project Labor Cost (Cum BL Project) then choose Edit | Copy, Figure 15.
Then, in Figure 16, after exercising the data in Excel, we have a graph with smoothed S-curves of our current budget versus the baseline.
In Figure 16, there is a noticeable improvement in “S” shape alignment in the current budget (orange plot) versus the baseline budget (blue plot). Our updated lump-sum cost-loading distribution is better aligned with that of a realistic, successful project.
Summary
Schedulers can graph cost-loading histograms and S-curves of their schedule in P6 Professional. Use the Month/Week Timescale to eliminate flat lines in the S-curve plot on non-workdays (weekends). Plot two cumulative budget (baseline and current) S-curves on one graph using the Activity Usage Profile in the Bottom Layout tool group.
This enables you to make comparison-informed adjustments to your schedule to better achieve a true S-shaped cost-loading, which is more indicative of project spending across the lifecycle.